1. Field of the Invention
The invention relates to a disc recliner for an automotive vehicle seat that allows pivotal adjustment of a seat back relative to a seat cushion. More particularly, the invention relates to a continuous disc recliner having an anti-backdrive mechanism.
2. Description of Related Art
Automotive vehicles include seat assemblies for supporting a seated occupant in the vehicle. Each seat assembly includes a generally horizontal seat cushion and a generally vertical seat back operatively coupled to the seat cushion by a recliner assembly. The recliner assembly allows for adjustment of the seat back relative to the seat cushion between a plurality of reclined seating positions.
One well known type of recliner assembly includes a pair of continuous disc recliners to operatively couple the seat back to the seat cushion. Generally, a typical prior art continuous disc recliner includes a fixed plate secured to the seat cushion and a movable plate secured to the seat back and rotatably coupled to the fixed plate. The fixed plate is formed to include a toothed outer profile and the movable plate is formed to include a toothed inner profile. The tooth count of the toothed outer profile has at least one less tooth than the tooth count of the toothed inner profile. A drive mechanism is disposed between the movable plate and the fixed plate and is operable for urging the movable plate to rotate relative to the fixed plate. The drive mechanism includes a cam and a pair of wedges that define an eccentric, which presses the toothed outer profile and the toothed inner profile into each other at an engagement point defined by the eccentricity. When the cam is rotated in a first direction, the wedges are driven in the first direction causing the direction of the eccentricity to shift and therefore shifting the engagement point of the toothed outer profile in the toothed inner profile. The shifting of the engagement point manifests itself as a wobbling rotational movement of the movable plate in the first direction, thereby reclining the seat back. When the cam is rotated in a second direction, the wedges are driven in the second direction causing the direction of the eccentricity to shift and therefore shifting the engagement point of the toothed outer profile in the toothed inner profile. The shifting of the engagement point manifests itself as a wobbling rotational movement of the movable plate in the second direction, thereby inclining the seat back. The seat back is maintained in a desired reclined seating position due to friction between the toothed outer profile and the toothed inner profile at the engagement point and due to friction between the wedges and the fixed and movable plates.
One drawback of this type of continuous disc recliner is back-driving. Back-driving is unwanted operation of the disc recliner in response to an external load placed against the seat back. In other words, when an occupant is seated on the seat assembly the external load against the seat back may overcome the friction that maintains the seat back in the desired reclined seating position. In such instances, the external load overcomes the friction and urges the movable plate in the first direction, thereby reclining the seat back.
It is desirable, therefore, to provide a continuous disc recliner with an anti-backdrive mechanism that prevents unwanted back-driving of the continuous disc recliner to maintain a seat back in a desired reclined seating position.